libhugs-haskell98-bundled 98.200609.21-5.4build1 / usr / lib / hugs / packages / haskell98 / IO.hs

module IO (
    Handle, HandlePosn,
    IOMode(ReadMode,WriteMode,AppendMode,ReadWriteMode),
    BufferMode(NoBuffering,LineBuffering,BlockBuffering),
    SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd),
    stdin, stdout, stderr, 
    openFile, hClose, hFileSize, hIsEOF, isEOF,
    hSetBuffering, hGetBuffering, hFlush, 
    hGetPosn, hSetPosn, hSeek, 
    hWaitForInput, hReady, hGetChar, hGetLine, hLookAhead, hGetContents, 
    hPutChar, hPutStr, hPutStrLn, hPrint,
    hIsOpen, hIsClosed, hIsReadable, hIsWritable, hIsSeekable,
    isAlreadyExistsError, isDoesNotExistError, isAlreadyInUseError, 
    isFullError, isEOFError,
    isIllegalOperation, isPermissionError, isUserError, 
    ioeGetErrorString, ioeGetHandle, ioeGetFileName,
    try, bracket, bracket_,

    -- ...and what the Prelude exports
    IO, FilePath, IOError, ioError, userError, catch, interact,
    putChar, putStr, putStrLn, print, getChar, getLine, getContents,
    readFile, writeFile, appendFile, readIO, readLn
  ) where

import System.IO
import System.IO.Error

-- | The 'bracket' function captures a common allocate, compute, deallocate
-- idiom in which the deallocation step must occur even in the case of an
-- error during computation. This is similar to try-catch-finally in Java.
--
-- This version handles only IO errors, as defined by Haskell 98.
-- The version of @bracket@ in "Control.Exception" handles all exceptions,
-- and should be used instead.

bracket        :: IO a -> (a -> IO b) -> (a -> IO c) -> IO c
bracket before after m = do
        x  <- before
        rs <- try (m x)
        after x
        case rs of
           Right r -> return r
           Left  e -> ioError e

-- | A variant of 'bracket' where the middle computation doesn't want @x@.
--
-- This version handles only IO errors, as defined by Haskell 98.
-- The version of @bracket_@ in "Control.Exception" handles all exceptions,
-- and should be used instead.

bracket_        :: IO a -> (a -> IO b) -> IO c -> IO c
bracket_ before after m = do
         x  <- before
         rs <- try m
         after x
         case rs of
            Right r -> return r
            Left  e -> ioError e